Conventional UV systems include one or more magnetrons and a UV bulb. Upon the application of power, the magnetrons generate RF energy that is transmitted to the UV bulb through a waveguide, thereby igniting a gas within the UV bulb and causing the gas to enter into a plasma state. As a result of this excitement, the UV bulb begins to emit UV energy, which is then used for various applications. For example, the UV energy can irradiate a substrate for purposes of curing materials thereon or for other reasons, such as surface treatment. Materials, such as inks or adhesives for example, may be cured on the substrate by directing the emitted UV energy onto the materials. As another example, the UV energy can be directed at the substrate to modify the surface thereof.
In such conventional UV systems, high powered magnetrons are required to achieve adequate RF energy for causing the gas in the UV bulb to enter into the plasma state. The one or more magnetrons are typically enclosed in a lamphead with the UV bulb. If more than one magnetron is used, the frequencies of the RF energy generated by the magnetrons must be far enough apart to prevent one magnetron from damaging or interfering with another, but at the same time must be sufficient for adequately exciting the UV bulb. Consequently, implementation of multiple magnetrons within one lamphead, especially implementing more than two magnetrons, causes operational problems and reduced effectiveness. This is because when multiple magnetrons are used, a broader range of RF frequencies is required. Some frequencies in the range have reduced effectiveness in exciting the UV bulb.
Within the conventional lamphead, the UV bulb is mounted within a metallic microwave cavity or chamber and located at the focal point of a parabolic reflector. During operation, RF energy produced by the magnetrons travels through the waveguide to the microwave cavity or chamber, thereby causing the UV bulb mounted therein to ignite and emit UV energy as described above. For this prior art lamphead configuration to be viable, precise cooling of the lamphead is required to sufficiently remove heat produced by the magnetron and provide a proper distribution of cooling air over the length of the UV bulb. Cooling must be precise because undercooling the magnetron or UV bulb can cause permanent damage to these components, and overcooling the UV bulb can adversely affect the UV output or even extinguish the bulb, thereby causing the gas of the bulb to separate and consequently preventing the bulb from being re-started. Because of the volume of air that is needed to adequately cool both the magnetrons and the UV bulb, conventional UV lampheads typically incorporate air blowers and specifically designed plenums. Due to factors such as cooling and bulb starting, tapered UV bulbs are used having a narrower diameter in the center region than at the end regions. This particular bulb shape helps compensate for the balancing act between cooling the magnetrons without overcooling the UV bulb. However, such a shape increases both the complexity and cost of manufacturing the UV bulb.
The configuration of the lamphead used in conventional UV systems has additional challenges. For example, the use of magnetrons and their containment in the lamphead with the UV bulb causes the overall system to have a power efficiency of about 70-80%, partly due to the unstable RF output that is characteristic of magnetrons and to the cooling requirements discussed above. In addition, such a lamphead configuration causes an increase in the required size and weight of the lamphead. Furthermore, because magnetrons are slow to start and stop, conventional UV systems often incorporate a starter bulb within the lamphead. The starter bulb is powered at the same time the magnetrons are initially energized and helps the UV bulb to ignite faster, thereby allowing the prior art UV system to begin producing UV energy faster. The starter bulb further increases the size of the lamphead and power consumption.
In addition, to produce maximum UV energy from a UV bulb it is necessary to uniformly distribute the RF energy along the length of the bulb. Furthermore, the intensity of emitted UV energy largely depends on the RF energy applied to the UV bulb. Although the waveguides used in conventional UV systems help distribute the RF energy produced by the magnetrons across the length of the bulb, such waveguides have a fixed geometry and require a standing wavelength directly proportional to a magnetron's output frequency. Because the magnetrons do not provide a highly stable or finely tunable RF output frequency, inefficient RF energy coupling and uneven irradiation of the UV bulb may occur.
Magnetrons also have a limited life span because of filament degradation over time. When used as part of the conventional UV system, the life of a magnetron may be as low as 1,000 hours. The limited life of magnetrons is a concern, as the down time from replacing dead magnetrons can be expensive. As a result, aggressive maintenance schedules are often implemented to replace magnetrons before they fail, and this further adds to costs.
For these reasons, as well as others, it would be desirable to provide UV systems and methods that improve upon areas such as power efficiencies, output, versatility, and component lifespan.